The present invention relates to optical bar code readers and includes an optical signal processor for both detecting and reading bar code labels on objects and detecting the presence or absence of the objects themselves.
Fixed scan bar code readers are often used in such environments as production plants and scientific research laboratories to automatically take an inventory of items transported by automatic conveyance passed a fixed optical scanner. For example, in laboratory studies, pharmaceutical testing and production plants it is often necessary to make a careful inventory of each compound held in a vessel such as a test tube where hundreds of such compositions and their containers are handled by automated or semi-automated equipment. A bar code label on each vessel such as a test tube has been found to be a reliable and highly efficient expedient to maintain the necessary inventory control over the compounds. The fixed scanners are placed alongside a line array of vessels that are transported across the path of the fixed optical scanner. The bar codes, when presented to the scanner, are read automatically and the resulting label information is fed to data processing equipment for identifying that particular vessel, its compound, and other pertinent data.
In such an environment, to maintain the high integrity of production and scientific control, it is desirable to know when a particular object is present or absent at each retention location. For example, the automated equipment may transport a single file line-up of test tubes past the scanner. A transportable rack is provided with test tube holders. When any of these holders, which may simply be a receiving hole in a rack, is empty, that information is useful in order to take an accurate inventory of the vessels present and their respective bar codes.
Therefore, it is an aspect of the present invention to incorporate, in a bar code scanning and reading system, a device for sensing the presence or absence of the object itself, especially objects having a reflectivity that is significantly different compared to that of the bar code label, such as transparent or translucent glass, ceramic, plastic, or other similar materials. In some existing systems, efforts have been proposed to determine whether an object is present or absent from the processing of the bar code label data. For example, using known bar code verification techniques including code matching algorithms, it is possible to verify that a valid label has been read and in such case it is presumed that the object is present. If only fragments of bar code data are detected, the signal processing presumes that a label or part of a label was present, even though unreadable or unverifiable, and that therefore the object is also present. As the retrieved bar code fragments diminish below a certain threshold level it is assumed that no label is present and in such case it is unknown or at least uncertain as to whether the object is present. When the presence or absence of the object, such as a test tube, is unknown or at least uncertain, the ability of the system to provide accurate inventory and quality control is diminished.